NASA Logo

NTRS

NTRS - NASA Technical Reports Server

Back to Results
Anti-Adhesion Elastomer Seal Coatings for Ultraviolet and Atomic Oxygen ProtectionRadiation blocking sunscreen coatings have been developed for the protection of elastomer seals used in low-Earth-orbit (LEO). The coatings protect the seals from ultraviolet (UV) radiation and atomic oxygen (AO) damage. The coatings were developed for use on NASA docking seals. Docking seal damage from the UV and AO present in LEO can constrain mission time-line, flight mode options, and increases risk. A low level of adhesion is also required for docking seals so undocking push-off forces can be low. The coatings presented also mitigate this unwanted adhesion. Greases with low collected volatile condensable materials (CVCM) and low total mass loss (TML) were mixed with slippery and/or UV blocking powders to create the protective coatings. Coatings were applied at rates up to 2 milligrams per square centimeter. Coated seals were exposed to AO and UV in the NUV (near-UV) and UV-C wavelength ranges (300 to 400 nanometers and 254 nanometers, respectively). Ground based ashers were used to simulate the AO of space. The Sun's UV energy was mimicked assuming a nose forward flight mode, resulting in an exposure rate of 2.5 megajoules per square meter per day. Exposures between 0 and 147 megajoules per square meter (UV-C) and 245 megajoules per square meter (NUV) were accomplished. The protective coatings were durable, providing protection from UV after a simulated docking and undocking cycle. The level of protection begins to decline at coverage rates less than 0.9 milligrams per square centimeter. The leakage of seals coated with Braycote plus 20 percent Z-cote ZnO sunscreen increased by a factor of 40 after moderate AO exposure; indicating that this coating might not be suitable due to AO intolerance. Seals coated with DC-7-16.4 percent Z-cote ZnO sunscreen were not significantly affected by combined doses of 2 x 10 (sup 21) atoms per square AO with 73 megajoules per square meter UV-C. Unprotected seals were significantly damaged at UV-C exposures of 0.3 megajoules per square meter and DC-7-16.4 percent Z-cote coated seals were undamaged at all exposures up to the limits tested thus far which were 147 megajoules per square meter UV-C and 245 megajoules per square meter NUV. The coatings decreased adhesion sufficiently for docking seals at temperatures equal to or greater than -8 degrees Centigrade thus offer a simple and inexpensive way to mitigate adhesion.
Document ID
20150002702
Document Type
Technical Memorandum (TM)
Authors
De Groh, Henry C., III (NASA Glenn Research Center Cleveland, OH United States)
Puleo, Bernadette J. (NASA Glenn Research Center Cleveland, OH United States)
Waters, Deborah L. (NASA Glenn Research Center Cleveland, OH United States)
Miller, Sharon K. (NASA Glenn Research Center Cleveland, OH United States)
Date Acquired
March 10, 2015
Publication Date
February 1, 2015
Subject Category
Spacecraft Design, Testing and Performance
Space Radiation
Mechanical Engineering
Report/Patent Number
E-18933-1
NASA/TM-2014-218334 Rev1
GRC-E-DAA-TN19443
Funding Number(s)
WBS: WBS 871056.06.02.01.09.02
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.
Keywords
adhesion
O ring seals
Silicones
Low Earth Orbit
exposure
docking
Ultraviolet radiation

Available Downloads

NameType 20150002702.pdf STI